Gelman R A, Poppke D C, Piez K A
J Biol Chem. 1979 Nov 25;254(22):11741-5.
We showed previously that fibril formation in vitro from rat tail tendon collagen requires a temperature-dependent initiation (Step 1) following which linear assembly to form thin filaments (Step 2) proceeds as rapidly at 4 degrees C as at 26 degrees C. Step 3, lateral assembly of filaments to form fibrils, is again temperature-dependent. We now find that Step 1 is complete in 6 min at 26 degrees C and the time is independent of collagen concentration in the range 0.08 to 0.39 mg/ml. Collagen treated with pepsin, which removes the nonhelical ends but leaves the triple helix intact, forms fibrils by a similar mechanism. However, Step 1 is altered or absent and early temperature changes produce a complex response consistent with an alternate, counterproductive pathway. Assembly is also much slower, particularly Step 2, and the fibrils formed are abnormal in that native banding is often absent and short tactoidal forms are common. These results suggest that in the assembly of fibrils from normal collagen the nonhelical ends are involved in an early conformational change and critically regulate later steps.
我们之前表明，大鼠尾腱胶原蛋白在体外形成原纤维需要一个温度依赖性的起始步骤（步骤1），在此之后，线性组装形成细丝（步骤2）在4℃和26℃下进行的速度一样快。步骤3，细丝的侧向组装形成原纤维，同样是温度依赖性的。我们现在发现，步骤1在26℃下6分钟内完成，且该时间与胶原蛋白浓度在0.08至0.39mg/ml范围内无关。用胃蛋白酶处理的胶原蛋白，去除了非螺旋末端但保留了三螺旋完整，通过类似的机制形成原纤维。然而，步骤1发生改变或不存在，早期温度变化产生与另一种适得其反的途径一致的复杂反应。组装也慢得多，特别是步骤2，并且形成的原纤维是异常的，因为通常不存在天然条纹，短的类晶体形式很常见。这些结果表明，在由正常胶原蛋白组装原纤维的过程中，非螺旋末端参与早期构象变化并关键地调节后续步骤。
